Please read the DLC page carefully and try not to spread misinformation in the comment section. There is currently a free version of the DLC which includes all the original 18+ scenes from the game, and it has always been available to download since the first major update (and release of the 18+ DLC). You do not need to pay for it and it will always remain free. This is also specified in the "Day 5.5" devlog on Itch.
The paid version of the DLC, however, offers bonus content that is entirely new such as top, bottom, and verse variations, new encounters and dialogue options, additional 18+ scenes, and eventually new CG art. Again, the DLC page outlines the differences between the free and paid version if you'd like to know more.
Lastly, as other commenters have said, the paid version is locked behind a price tag to discourage minors from accessing it, to offer a way to support the creator, and to help provide the funding needed for future updates like voice acting and language translations. Please keep in mind that 14DWY is an indie project developed by one person, and she is offering the full game, its future updates, and the original 18+ scenes to the public for free. While you are not obligated to spend $2 on the paid version of the DLC, you've always had the option to use the free version at no cost at all. So please do not spread misinformation about there being no free option available.